Mass production of ophthalmic lenses, in particular of contact lenses such as soft contact lenses, is usually performed in a fully automated process. Such process is described, for example, in WO 98/42497. In an embodiment of this fully automated process the contact lenses are manufactured with the aid of reusable molds comprising male and female mold halves. In a first processing station, a lens forming material is introduced into the female mold halves. A lens forming material known to be useful in such process is a prepolymer solution including prepolymers based on polyvinyl alcohols (PVA). The molds are then assembled in a subsequent processing station with the aid of corresponding male mold halves to form a mold cavity defining the shape of the contact lens to be formed. In a yet further subsequent processing station, the starting material within the mold cavity is polymerized and/or crosslinked by irradiation with ultraviolet radiation (UV-radiation) to form the soft contact lenses. Those portions of the lens forming material contained in the mold cavity which are not to be exposed to UV-radiation are shielded by a metal mask, which is arranged to surround the lens forming surface, so that the mask limits the space where the lens forming material enclosed between the male and female mold halves is exposed to UV-radiation. After exposure, the molds are opened and the so formed contact lenses are removed from the male or female mold halves, respectively, and are subsequently transported to further processing stations.
As has been outlined above, mass production of ophthalmic lenses includes the use of reusable molds or mold halves, respectively. The reusable molds or mold halves, or at least those parts thereof comprising the lens forming surfaces, are typically made from optically finished glass, for example from quartz glass. Such reusable molds are advantageous since they are transparent to UV-radiation, durable, can be easily cleaned after molding for subsequent re-use, etc. Therefore, they are particularly suitable for multiple use in mass production of ophthalmic lenses. However, depending on the lens forming material used, opening of the molds and subsequent removal of the contact lenses from the male or female mold half may turn out to be a task which is difficult to perform.
For example, when using lens forming materials for forming silicon hydrogel (SiHy) contact lenses, which are known to have excellent properties regarding oxygen permeability, wearing comfort, etc., considerably high forces are needed for opening the molds, that is to say for the separation of the male and female mold halves after the SiHy contact lens is formed by exposure to UV-radiation. Also, the adhesive forces between the lens forming surfaces and the formed SiHy contact lens may be very high. That is to say, even after opening of the molds the SiHy contact lens may strongly adhere to the lens forming surface of the male or female mold half, so that it is difficult to remove the contact lens from the mold half without damaging the lens (e.g. causing tears, starburst fractures, etc.). Accordingly, without further measures the result may be an increased number of damaged contact lenses which cannot be distributed to the consumers but must be disposed of. This may lead to an unacceptably high reject rate and may substantially affect the efficiency of the mass production process.
EP-0 686 469 and EP-0 740 997 suggest to apply a thin layer or film of a polymeric surfactant to an annular flange region extending about a mold surface of a plastic mold half. The thin layer of surfactant is supposed to facilitate removal of excess polymeric material (HEMA) which forms a ring extending externally of the mold cavity. With respect to SiHy contact lenses it has been suggested that the lens forming materials be provided with one or more mold release agents that should allow the more simple removal of the SiHy contact lens from the respective mold half, see WO 2009/085902. However, these mold release agents must be specifically adapted (tailored) to the respective lens forming material used to form the SiHy contact lens. In addition, even when using such mold release agents the above-mentioned problems related to the considerably high forces for separating the mold halves and related to the strong adhesive forces of the SiHy lens to the male or female mold half may continue to occur.
It is therefore and object of the present invention to provide a remedy to the afore-mentioned problems of the prior art. In particular, a method shall be provided which facilitates separation of the mold halves and/or removal of the ophthalmic lens from the respective lens molding surface of the mold half to which the molded ophthalmic lens adheres, even in cases where the ophthalmic lenses are made from lens forming materials such as SiHy materials or other materials, which tend to strongly adhere to the lens molding surfaces of reusable glass molds or mold halves. Preferably, the method shall be capable of being fully integrated in automated continuous mass production processes of ophthalmic lenses, in particular contact lenses and especially soft contact lenses made from such materials.